Circuit interrupter with triggered vacuum gap

ABSTRACT

An electrical system in which a current zero occurs comprises a pair of circuit breaker contacts between which an arc is established during contact separation. A triggerable vacuum gap is arranged in parallel with the separable contacts and means responsive to system conditions trigger the gap and cause it to break down while arcing occurs between the contacts but shortly before current zero thereby starving the circuit breaker arc and permitting rapid extinction of the spark gap arc.

United States Patent [72] 2,610,231 9/1952 Wettstein 317/11 N w n. s-2,789,253 4/1957 Vang 317/11.4 [21] Appl. No. 884,147 3,243,656 3/1966Baude 317/11 [22] Filed Dec. 11, 1969 3,275,891 9/1966 Swanson.. 317/16[45] Patented JIIM 15, 1971 3,309,575 31196? Lee 317/50 [73] AssigneeAllis-Chalmers Manufacturing Company 3,328,632 6/1967 Robinson 317/62Milwaukee, Wis. 3,430,016 2/1969 l-lurtle 317/11 3,454,832 7/1969 Hurtle317/11 541 CIRCUIT INTERRUPTER wm1 TRIGGERED Primary Hammer-MiltonHirshfield VACUUM GAP Assistant Exammer- Ulysses Weldon I 7 Chin 2Drawing Figs Attorneys--Thomas F. Kirby, Lee H. Kaiser and Robert B.

Benson [52] US. Cl 317/11, 307/136 h 1 Int. An electrical system in acurrent zero 0e. of Search l, 16, curs com rises a pair of circuitbreaker contacts between 1 7L 50; 200/146 which an arc is establishedduring contact separation. A triggerable vacuum gap is arranged inparallel with the separable [56] References cued contacts and meansresponsive to system conditions trigger UNITED STATES PATENTS the gapand cause it to break down while arcing occurs 3,087,092 4/1963 Lafferty315/330 between the contacts but shortly before current zero thereby3,515,940 6/1970 Hobson,.1r. 317/11 starving the circuit breaker arc andpermitting rapid extinc- 1,595,768 8/1926 Eschholz 317/1 1 tion of thespark gap arc.

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CIRCUIT INTERRUPTER WITH TRIGGERED VACUUM GAP BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates generally tomeans for interrupting electric circuits and, particularly, to suchmeans which employ triggered vacuum gaps in conjunction with circuitinterrupters.

2. Description of the Prior Art Efforts are continually underway toupgrade the interrupting performance of electric circuit interrupters,particularly those handling high voltage alternating current or DCinterrupters with artificially introduced current zeros. For example,U.S. Pat. No. 3,243,656 owned by the same assignee as the presentapplication teaches, among other things, a control for a circuitinterrupter whereby the interrupter contacts are opened shortly before apredictable current zero to reduce contact erosion and increase theinterrupting capacity of the breaker.

Conventional circuit breakers, such as oil, air and gas blast, airmagnetic, and other types, develop a relatively high are voltage rangingfrom about 100 volts to several kilovolts. These breakers have arelatively long dielectric recovery time after the arc has beenextinguished at current zero. The advantage of conventional'br'eakers isthat they can handle the very high short circuit currents which areencountered in modern high power electric circuits. Yet, therelativelylong dielectric recovery time makes them susceptible torestrike after current zero. It is known that a vacuum arc ischaracterized by a low arc voltage and by an extremely short dielectricrecovery time..A vacuum spark gap can be fired with high precision intime either by an electric signal or by a laser beam pulse, for example.In accordance with the present invention, the rather high arc voltagedeveloped by conventional breakers allows a transfer of the arc from theconventional breaker to a vacuum spark gap at a certain time intervalbefore current zero.

SUMMARY OF THE INVENTION In accordance with the present invention, thereis provided an electrical system or circuit in which a current zerocondition exists. The current zero condition may be natural, as in thecase of alternating current, or it may be artificially introduced into adirect current system for interruption purposes. The system comprises apair of circuit breaker contacts between which an arc is establishedupon contact separation. A triggerable vacuum gap is arranged inparallel with the separable contacts and means responsive to systemconditions trigger the gap and cause it to break down while arcingoccurs between the contacts but shortly before current zero, therebystarving the circuit breaker arc and permitting rapid extinction of thevacuum-gap arc.

In accordance with the present invention, the characteristics ofconventional breakers and of vacuum spark gaps are combined in order toutilize their individual strengths while overcoming their individualweaknesses and providing new, improved and unobvious results.Conventional breakers are well developed for handling high short circuitcurrents. Their weakness is a relatively long dielectric recovery time.They develop a relative high are voltage. This allowsthe transfer of thearc to a vacuum spark gap within a short time interval before currentzero. This time interval is chosen so that the transferred arc currentis on the order of some desired value of kiloamperes. The extremelyshort dielectric recovery time of the vacuum gap may thus be utilizedwithoutsu bjecting the vacuum arc to the full magnitude of current to beswitched.

2 OBJECTS OF'THE INVENTION It is an object of the present invention toprovide improved means to upgrade the arc interrupting ability ofelectric circuit breakers, to reduce contact erosion therein, and toincrease breaker ratings.

Another object is to provide improved means of the aforesaid characterwhich are adaptable for use with many types of circuit breakers,including oil breakers, air or gas blast breakers, and air magneticbreakers.

Another object is to provide improved means of the aforesaid characterwhich employ components which have already been developed and arecommercially available.

Another object is to .provide means of the aforesaid character which arerelatively inexpensive, reliable in use and have a long working life.

Other objects and advantages of the invention will hereinafter appear. 1

DESCRIPTION OF THE DRAWING The accompanying drawing illustrates apreferred embodiment of the invention but it is to be understood thatthe embodiment illustrated is susceptible of modifications with respectto details thereof without departing from the scope of the appendedclaims.

In the drawing:

FIG. 1 shows a schematic diagram of an electric circuit embodying thepresent invention; and

FIG. 2 is a graph of current conditions in the circuit duringinterruption.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of thedrawing, there is shown a circuit wherein the numeral 10 designates asource of high voltage current from which a load 12 is energizablethrough a powerline 14.

In accordance with the invention, the electrical system or circuit isone in which a current zero condition exists. For example, the currentzero condition may be natural, as in the caseof alternating current fromsource 10, or it may be artificially introduced into a direct currentsupply from source 10 for interruption purposes by well-known means.

Connection and disconnection of load 12 to and from source 10 iscontrolled by circuit interrupting means such as a circuit breaker 16which comprises a pair of separable relatively movable contacts 16a and16b which are connected in line 14. Contact 16b (shown in opencondition) for example, is movable to contact closed and contact openpositions by contact operating means, such as a contact operatingmechanism 18. It is to be understood, for example, that operatingmechanism 18 effects opening of the contacts 16a and 16b in response tooperation of a condition responsive means 20 which senses faults andother conditions, such asexcessive current flow, in line 14 when thesystemis in operation. When contacts 16a and 16b of circuit breaker 16are separated by operating mechanism 18 in response to a fault conditionin line 14 sensed by condition responsive means 20, an arc isestablished between the contacts which must be extinguished as rapidlyas possible.

In accordance with the present invention, a trig'gerable spark gapdevice 22, having a lower arc voltage characteristic than main breakerl6 and fast dielectric recovery, preferably of the vacuum type, isconnected in parallel circuit with circuit breaker l6. Spark gap device22 comprises a pair of spacedapart electrodes 22a and 22b which aredisposed in a housing 22d in which a vacuum is maintained. Spark gapdevice 22 further comprises triggering means 220 to effect breakdown ofthe gap between the electrodes 22a and 22b. US. Pat. No. 3,303,376teaches a triggered vacuum gap device of a type suitable for use in thepresent invention but other triggerable vacuum gap devices could beused. Spark gap device 22 is connected in parallel with.circuit breaker16. More specifically, electrodes 22a and 22b of device 22 areelectrically connected to contact 16a and 16b, respectively, of circuitbreaker 16. The triggering means 220 of spark gap 22 is connected to acondition responsive means 24 which is adapted to sense conditions, suchas current flow conditions, in line 14 and effect firing or breakdown ofspark gap device 22 slightly before zero current while arcing existsbetween contacts 160 and 16b of circuit breaker 16. US. Pat. No.3,243,656 teaches a control for sensing line conditions and forproviding a control signal at a predetermined point in the current orvoltage waveform, such as at current zero or other desirable point,which control is adaptable to fire or trigger a device such as device22. Condition responsive means 24 effects breakdown of trigger device 22at some point in the interval of one-quarter of a cycle (4.1milliseconds) before current zero, but preferably shortly before currentzero when the current magnitude does not exceed the value of somepredetermined value of KA,

such as IOKA, for example, as shown in the graph FIG. 2.

A system in accordance with the invention operates as follows. Assumethat contacts 16a and 16b of circuit breaker 16 are closed and that load12 is being energized from source 10. Further assume that a faultcondition occurs in line 14 and that condition responsive means 20senses the fault and thereby causes operating mechanism 18 to effectopening of contacts 160 and 16b of circuit breaker 16. As the contacts16a and 16b separate, a high current arc accompanied by high are voltageis established therebetween. Further assume that condition responsivemeans 24 also senses the fault condition and produces an output signalwhich effects breakdown of the gap between the electrodes 22a and 22b ofspark gap device 22 sometime within one-quarter of a cycle before thefirst current zero and preferably at the point shown in the graph inFIG. 2. When this occurs, the arc voltage in device 22 is much lowerthan that in circuit breaker l6 and, thus, the are between contacts 16aand 16b of the circuit breaker is completely starved and extinguishedand, in effect, transferred to device 22. However, because the vacuumgap device 22 has excellent dielectric recovery characteristics, the arctherein is readily extinguished when the current zero condition isreached in device 22. After the arcs in circuit breaker l6 and device 22have been extinguished, the contacts 16a and 16b of the circuit breakerare ready to be reclosed by operating mechanism 18 in readiness forsubsequent circuit interrupting operations.

In the embodiment shown, condition responsive means 20 and 24 are shownas separate elements. However, it is to be understood that at least someportions of these elements perform similar functions and could becombined, such a means common to both for sensing current flowconditions in line 14, for example. 1

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

lclaim: 1. In combination, an electrical circuit in which a current zerocondition occurs, at least a pair of separable contacts in said circuit,triggerable spark gap means shunting said pair of contacts and having alower arc voltage characteristic and shorter dielectric recovery timethan said pair of separable contacts, first means to effect separationof said pair of contacts whereupon arcing occurs between said pair ofcontacts, and second means for sensing and responding to conditions insaid alternating current circuit to effect triggering of said spark gapmeans to effect full transfer thereto of arcing which occurs betweensaid pair of contacts at a point in time less than one-quarter cycleprior to occurrence of a current zero in the are. 2. A combinationaccording to claim 1 wherein said triggerable spark gap means comprisesspaced-apart electrodes which are disposed in a vacuum.

. A combination according to claim 2 wherein said first means isresponsive to conditions in the electrical circuit and effects contactseparation of said pair of contacts in response to a fault condition.

4. A combination according to claim 3 wherein said first means andsecond means have common means for sensing conditions in said circuit.

5. A combination according to claim 3 wherein said circuit comprises asource of current, a line and a load, wherein said pair of separablecontacts are comprised in a circuit interrupting device and are disposedin said line between said source and said load, wherein each one of saidspark gap electrodes is electrically connected directly to one of saidcontacts, and wherein said spark gap means comprises a trigger electroderesponsive to an output signal from said second means.

6. A combination according to claim 5 wherein said second means isadapted to provide an output signal to said trigger electrode at aselectable predetermined time within onequarter cycle prior to theoccurrence of the first current zero.

7. A combination according to claim 1 wherein triggering of said sparkgap and transfer of the arc thereto from said pair of contacts occurs ata time within said one-quarter cycle when current magnitude does notexceed IOKA.

1. In combination, an electrical circuit in which a current zerocondition occurs, at least a pair of sepaRable contacts in said circuit,triggerable spark gap means shunting said pair of contacts and having alower arc voltage characteristic and shorter dielectric recovery timethan said pair of separable contacts, first means to effect separationof said pair of contacts whereupon arcing occurs between said pair ofcontacts, and second means for sensing and responding to conditions insaid alternating current circuit to effect triggering of said spark gapmeans to effect full transfer thereto of arcing which occurs betweensaid pair of contacts at a point in time less than one-quarter cycleprior to occurrence of a current zero in the arc.
 2. A combinationaccording to claim 1 wherein said triggerable spark gap means comprisesspaced-apart electrodes which are disposed in a vacuum.
 3. A combinationaccording to claim 2 wherein said first means is responsive toconditions in the electrical circuit and effects contact separation ofsaid pair of contacts in response to a fault condition.
 4. A combinationaccording to claim 3 wherein said first means and second means havecommon means for sensing conditions in said circuit.
 5. A combinationaccording to claim 3 wherein said circuit comprises a source of current,a line and a load, wherein said pair of separable contacts are comprisedin a circuit interrupting device and are disposed in said line betweensaid source and said load, wherein each one of said spark gap electrodesis electrically connected directly to one of said contacts, and whereinsaid spark gap means comprises a trigger electrode responsive to anoutput signal from said second means.
 6. A combination according toclaim 5 wherein said second means is adapted to provide an output signalto said trigger electrode at a selectable predetermined time withinone-quarter cycle prior to the occurrence of the first current zero. 7.A combination according to claim 1 wherein triggering of said spark gapand transfer of the arc thereto from said pair of contacts occurs at atime within said one-quarter cycle when current magnitude does notexceed 10KA.